1. Field of the Invention
The present invention relates to small internal combustion engines of the type used with lawnmowers, lawn and garden tractors, other small implements, or in sport vehicles, for example. In particular, the present invention relates to determining engine cycle recognition, or piston stroke recognition, in such engines for fuel delivery by a fuel injection system.
2. Description of the Related Art
Small internal combustion engines, such as single or two cylinder engines, are supplied with a fuel/air mixture for combustion via either a carburetor or by a fuel injection system in a conventional four cycle operation, including the piston strokes of intake, compression, power, and exhaust. In small engines which include a fuel injection system, it is important to determine the phase or stroke of the cylinder piston(s) in order to ensure that fuel is injected into the cylinders at the optimum point during the intake stroke of the piston(s).
In many known systems for determining piston stroke recognition, electronic sensors are used to sense the position of the engine crankshaft and/or camshaft. Signals generated from these sensors are used to coordinate the position and speed of the crankshaft or camshaft with the position of one or more pistons to determine when to inject fuel into the engine cylinders. Disadvantageously, these systems require separate sensors to be mounted to the engine, which tends to increase the overall cost and complexity of the fuel injection systems for small internal combustion engines.
Additionally, some small engines may experience high inertial loads during running, such as engines which drive a high inertia implement through a belt drive, for example. In these engines, it has been found that the inertia of the driven implement and the elasticity of the belt, for example, may impose a strong load on the engine crankshaft. At certain times during running the engine, this imposed load primarily determines the crankshaft speed, rather than the actual firing of the engine cylinders. Under these circumstances, piston stroke recognition methods which are dependent upon sensing crankshaft or camshaft speed may be prone to failure.
What is needed are piston stroke recognition methods for small internal combustion engines which are an improvement over the foregoing.